Performance Analysis of LNG Liquefaction Process Integrated with Allam Cycle Centered Power Plant

Liquefied Natural Gas (LNG) is an increasingly important clean energy source, which has been widely produced, transported, and consumed all over the world. Particularly in the US, the ambulant availability of natural gas enables many LNG liquefaction projects to be built in the following decade. In the meantime, the increasing trend to utilize the natural gas to generate power becomes an important element to monetarize the natural gas in the U.S. In this paper, an LNG liquefaction process and an Allam cycle centered power plant has been integrated for study. The power plant subsystem is the natural gas empowered complex, which includes a power plant driven by the Allam cycle to generate net power and pure CO₂ for commercial utilization; an air separation unit (ASU) to supply the pure oxygen to the power plant and the pure nitrogen as feed stock; as well as an ammonia plant to utilize the nitrogen to produce ammonia. The LNG liquefaction system is the propane pre-cooled mixed refrigerant process (C3MR), which involves pre-cooling of natural gas using propane refrigeration loop followed by sub-cooling and liquefaction in the second loop using a mixed refrigerant composed of methane, ethane, and propane.

Note that the nitrogen gas stream is a by-product from the ASU unit of the power plant subsystem, which is at a temperature of -25⁰C and can be used in the C3MR process for help pre-cooling operation in advance, and then be directed to the ammonia plant as the feed stock in order to save energy. In this paper, we have explored various opportunities of utilizing this nitrogen gas stream for helping the C3MR pre-cooling process. This study targets on maximizing the energy efficiency and minimizing the cost of production simultaneously. This integrated new process has been virtual demonstrated via simulation, which is economically sound, technological viable, and environmentally benign due to the comprehensively monetarized cheap natural gas resource to accomplish an integrated power-chemical-LNG process via heat, mass, and work integrations.